Cardiac pacemakers have been used to sense and pace heart rates for patients with a variety of incorrect heart rhythms, including but not limited to bradycardia, which is a slow heart rate. In some cases, a cardiac pacemaker may include a metal enclosure that contains control circuitry. Leads, which are electrically conductive, may be operatively coupled with the cardiac pacemaker and may extend into the circulatory system terminating in the heart. The leads often include pacing electrodes located at or near the distal end.
FIG. 1 shows a typical pacemaker system having a pacemaker can 10 and one or more leads, where only one lead 12 is shown in FIG. 1. Pacemaker can 10 is shown placed in a pocket in the upper chest area. The lead 12 is shown extending from the pacemaker can 10 and through the left subclavian vein, through the superior vena cava, and down into the patient's right ventricle, terminating in an electrode 14. In the example shown, the pacemaker can 10 is implanted external to the heart H while the lead 12 passes into the heart H, and places the electrode 14 at the ventricle wall of the heart H. In some cases, the lead 12 can be a potential weak link in the pacemaker system. Possible complications from the lead 12 may include displacement or misplacement of the lead 12, lead fracture or perforation, and pocket infections at or near the pacemaker can 10. In some cases, the lead 12 may impede certain surgical procedures by getting in the way.
Leadless pacemakers are in development, and enjoy the potential benefit of not including or using leads. As seen in FIG. 2, an example leadless pacemaker 16 is shown disposed within the patient's right ventricle. In some cases, the leadless pacemaker 16 may be self-contained, including a power supply such as a battery, control circuitry and one or more electrodes that may be disposed on an outer surface of the leadless pacemaker 16. The leadless pacemaker 16 is shown disposed entirely within the heart H, and more specifically in the right ventricle of the heart H. Because the battery life of the leadless pacemaker 16 often determines the useful life expectancy of the leadless pacemaker 16, the battery is often made to consume a relatively large fraction of the internal volume of the leadless pacemaker 16. There is a desire, however, to reduce the size of such leadless pacemakers, while at the same time increase their useful life expectancy.